Electrowetting might not be a term or a concept you are familiar with yet, but it is the principle behind optofluidic solar concentration, another one of the recent ARPA-E grants to improve efficiency in solar energy. Beyond that, it may be a part of technologies you will use in the next few years, and maybe even some you already have.
Solar power systems, particularly those aiming for high efficiency, cannot be fixed installations. An unmoving solar panel has its greatest efficiency when it is pointing directly toward the sun, and power production drops off significantly as the sun's angle becomes more and more oblique. Motors, actuators, and other mechanical control systems can be used to track the sun and keep the panels in optimal orientation. But these are expensive and require far more maintenance than do just the solar panels themselves.
Award winners Teledyne Scientific & Imaging in partnership with the University of Maryland are researching a system that will use an "electrowetting-based dynamic liquid prism" to focus the sun for concentrating solar collectors. Electrowetting is the principle where a liquid changes from beading up on a surface to flattening out, based on the application of an electric charge. Instead of needing a cumbersome system to track the sun, this will allow a thin layer on top of the photovoltaic material to track the sun without any moving mechanical parts. Or, as the ARPA-E information describes the system:
The electrowetting effect controls the contact angle of a liquid on a hydrophobic surface through the application of an electric field. With two immiscible fluids in a transparent cell, they can actively control the contact angle along the fluid-fluid-solid tri-junction line and hence the orientation of the fluid-fluid interface via electrowetting. The naturally-formed meniscus between the two liquids can function as an optical prism. Without any mechanical moving parts, this dynamic liquid prism allows the device to adaptively track both the daily and seasonal changes of the Sun’s orbit, i.e., dual-axis tracking.
In addition to the application for solar tracking, electrowetting may also be the technology that brings color to low-energy e-book readers. Small autofocus lenses, such as those used for cell phone cameras, also use electrowetting principles in the same way to control small lenses that are actually liquids.
Not only are the optofluidic systems likely to require less maintenance, they also require less energy for operation than mechanically moving the entire system, making them less parasitic of the power produced by the solar collector in the first place. Quieter, more reliable operation will also be a benefit for residential applications.
